Field of the Invention
The present invention relates to a display device, and more particularly, to a display device capable of having improved reliability by preventing the inflow of static electricity generated at the time of a scribing process.
Discussion of the Related Art
Recently, flat panel displays (FPDs) are becoming increasingly important with the development of multimedia. Accordingly, several display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), and an organic light emitting device (OLED) are used. Of theses, the organic light emitting display is being considered as a next-generation display device since the organic light emitting display has exhibits a high-speed response of 1 ms or less and low power consumption, and has self-light emission characteristics, causing no problems in the viewing angle.
The display device is driven in a passive matrix manner and an active matrix manner using thin film transistors. While the driving is implemented by forming positive electrodes and negative electrodes to cross each other and selecting a line according to the passive matrix manner, the driving is implemented by respectively connecting thin film transistors to pixels and maintaining a voltage through the capacitance of capacitors connected to gate electrodes of the thin film transistors.
Durability capable of keeping the lifespan and electric reliability as well as basic features of the thin film transistor, such as mobility and leakage current, are important for the thin film transistors. Here, an active layer of the thin film transistors is mainly formed of amorphous silicon or poly silicon. Amorphous silicon has advantages in that a film forming process is simple and the production cost is low, but a disadvantage in that electric reliability cannot be secured. In addition, poly silicon has disadvantages in that it is very difficult to implement a large-area application due to a high process temperature and the uniformity according to the crystallizing manner cannot be secured.
Meanwhile, in the case where the active layer is formed of an oxide, high mobility can be obtained even though the film is formed at a low temperature, and desired physical properties can be easily obtained since the change in resistance is large depending on the content of oxygen. Thus, the oxide is recently receiving a great attention in the application to the thin film transistor. Particularly, an example of the oxide usable in the active layer may be zinc oxide (ZnO), indium zinc oxide (InZnO), indium gallium zinc oxide (InGaZnO4), or the like. The thin film transistor including an active layer of oxide is unstable since the photocurrent is generated by an external light source, and thus a light shielding film for shielding the active layer from the external light is needed.
FIG. 1 is a plane view of a display device according to a related art; and FIG. 2 is a cross-sectional view cut along line IT of FIG. 1.
Referring to FIG. 1, a display device according to the art includes a plurality of display panels DP in which a plurality of active areas A/A are formed on a substrate 10 as a mother substrate. A scribing process is performed to separate respective independent panels from the formed display panels DP. According to the scribing process, the independent display panels DP are prepared by cutting the substrate 10 along scribing line {circle around (1)} and then cutting the substrate 10 along scribing line {circle around (2)} using a scribing wheel.
More specifically, referring to FIG. 2, a light shielding layer LS is disposed on the substrate 10, and a buffer layer 15 is disposed on the light shielding layer LS. The light shielding layer LS prevents the light from entering an active layer to be later formed. An active layer 20 is formed on the buffer layer 15, and insulated by a gate insulating film 25 disposed on the active layer 20. A gate electrode 30 is formed on the gate insulating film 25, and insulated by an interlayer film 35. A source electrode 40a and a drain electrode 40b are formed on the interlayer insulating film 35, and connected to the active layer 20 through contact holes 35a and 35b, thereby configuring a thin film transistor TFT. An organic insulating film 45 is disposed on the thin film transistor TFT. A pixel electrode 50 is disposed on the organic insulating film 45, and connected to the drain electrode 40b through a via hole 47. A bank layer 55 is disposed on the pixel electrode 50, and a light emitting layer 60 is disposed on the pixel electrode 50 exposed by the bank layer 55. A counter electrode 65 is disposed above the substrate 20 provided with the light emitting layer 60, and the resultant substrate is sealed with a counter substrate 70, thereby configuring a display device.
Meanwhile, as described above, the active layer 20 formed of an oxide is unstable since the photocurrent is generated by an external light, and thus the light shielding layer LS is formed on the entire surface of the substrate 20. However, during a scribing process, the static electricity generated when the substrate 20 is cut by a scribing wheel penetrates into the active area A/A through the light shielding layer LS, thereby influencing the thin film transistor. Therefore, electric characteristics of the thin film transistor are degraded, causing a deterioration in reliability.